MSB01 Architects Guide 2010-08-05 PDF

STEEL BUILDINGS IN EUROPE

Multi-Storey Steel Buildings

Part 1: Architect’s Guide

Multi-Storey Steel Buildings


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FOREWORD

This publication is the first part of the design guide, Multi-Storey Steel Buildings.

The 10 parts in the Multi-Storey Steel Buildings guide are:

Part 1: Architect’s guide

Part 2: Concept design

Part 3: Actions

Part 4: Detailed design

Part 5: Joint design

Part 6: Fire Engineering

Part 7: Model construction specification

Part 8: Description of member resistance calculator

Part 9: Description of simple connection resistance calculator

Part 10: Guidance to developers of software for the design of composite beams

Multi-Storey Steel Buildings is one of two design guides. The second design guide is Single-Storey Steel Buildings.

The two design guides have been produced in the framework of the European project “Facilitating the market development for sections in industrial halls and low rise buildings (SECHALO) RFS2-CT-2008-0030”.

The design guides have been prepared under the direction of Arcelor Mittal, Peiner Träger and Corus. The technical content has been prepared by CTICM and SCI, collaborating as the Steel Alliance.

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Contents Page No

FOREWORD i

SUMMARY v

1 INTRODUCTION 1

2 FUNCTIONAL QUALITIES 3 2.1 Architectural creativity and flexibility 3 2.2 Prefabrication – Industrialised building systems 5 2.3 An evolving art 6 2.4 Extending and refurbishment 6

3 STEEL – MATERIAL AND PRODUCTS 9 3.1 Steel the material 9 3.2 Steel products 9

4 BASIS OF GOOD DESIGN: THE STRUCTURE 13 4.1 The load-bearing system 13 4.2 Bracings 19 4.3 Floors 22 4.4 Connections 26 4.5 Summary 29

5 BASIS OF GOOD DESIGN: THE ENVELOPE 30 5.1 Façades 30 5.2 Roofing systems 36

6 OTHER FACTORS FOR GOOD DESIGN 41 6.1 Behaviour during an earthquake 41 6.2 Behaviour during a fire 42 6.3 Acoustic performance 48 6.4 Thermal performance 52 6.5 Durability of steel structures 53 6.6 Service integration 57

7 STEEL CONSTRUCTION AND SUSTAINABILITY 59 7.1 Life cycle 60 7.2 Advantages of steel products for construction 60 7.3 Steel-intensive solutions for buildings 61

8 CONCLUSION 64

REFERENCES 65

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SUMMARY

For centuries, steel has demonstrated all its advantages as a construction material for use in famous buildings in the world, but steel is not only a material that delivers technical prowess. It has so many qualities that simply make it the preferred material of architects, especially for multi-storey buildings. This publication has been drafted by architects for architects. It provides information on the material and on the industrial components. It gives the bases of good practice in order to achieve maximum benefit in using steel, in terms of structural behaviour of steel frames, the building envelope, acoustic and thermal performances and sustainable construction.

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1 INTRODUCTION

What do Claude Perrault’s Louvre colonnades (1670), Mies van der Rohe’s Lake Shore Drive apartment towers (1951), Soufflot’s Church of St. Genevieve in Paris (1759), Piano and Roger’s Georges Pompidou Centre (1977) and Jean Nouvel’s Hôtel Industriel in Pantin (1990) all have in common? Each one bears testimony to the great epic of metal in construction.

Of course, the transformation from iron used as structural reinforcement and decoration to the light and airy steel frame which we know today was a very long process. It encompassed no less than 300 years of historical progress, innovation, imagination and creativity: on the part of architects, who introduced new shape grammars with cast iron, iron and then steel; on the part of engineers, whose technical expertise and imagination played a major role in the building of new structures which were once thought of as impossible, even utopian; and on the part of manufacturers, who have worked tirelessly on the development of new materials and products.

Three hundred years of passion for metal: a passion which has been expressed in different ways. Cast iron, once used in buildings, was expensive, heavy and brittle, and provided a very special kind of structural reinforcement dictated by the style of that period: enormous proportions, with iron staples used to hold together blocks of stone to ensure the building’s stability.

Today’s enthusiasm for iron and steel is very different. Iron brought about transformations in design and the introduction of standard profiles (I, T and L). Thanks to riveting, profiles could be assembled in numerous ways to create all sorts of structures. A landmark achievement was Joseph Paxton’s Crystal Palace (1851), the predecessor of modular architecture with its prefabricated building components.

Figure 1.1 Crystal Palace, London

Steel has been in the vanguard of new assembly processes, rolling techniques and computational modelling. It has made possible the use of large spans in construction, for example in industrial buildings (La Samaritaine department store in Paris, which opened in 1917), and in infrastructure and transportation (The Forth Railway Bridge in Scotland, 1890).

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Steel is not just a material aimed at technical prowess! It has many qualities that make it the preferred material for architects. It is economical and provides great mechanical functionality; it permits the design of structures which are graceful, light and airy; it streamlines construction site processes; and offers rapid execution. A major advantage, however, is the infinite freedom for creation which it affords the architect. The combinations of different products lend themselves to rich and varied types of construction. When combined with glass, steel makes fabulous use of light and space.

This document, which is aimed at architects, provides an overview of the advantages of steel in construction for multi-storey buildings as well as best practice for this type of structure. Whatever the architect’s project, residential buildings, offices, schools, cultural buildings, retail or industrial buildings, the designer should read this document. It addresses:

The material, its qualities and market products

The structure (how to design)

The envelope (different types of façade and roofs, how to integrate solar panels etc.)

Sustainable steel construction.

Figure 1.2 Office building in Paris

Illustration of the many opportunities for using steel in building construction can be found on the following web sites:

www.access-steel.com

www.acierconstruction.com (in French)

www.construiracier.fr (in French)

www.infosteel.be (in French and Dutch)

www.bouwenmetstaal.nl (in Dutch)

www.bauforumstahl.de (in German)

www.sbi.se (in Swedish)

www.szs.ch (in French and German)

www.apta.com.es (in Spanish)

www.promozioneacciaio.it (in Italian)

www.eurobuild-in-steel.com

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2 FUNCTIONAL QUALITIES

2.1 Architectural creativity and flexibility Construction methods bring about new architectural, aesthetic and artistic solutions, breaking free of traditional practice. Awareness of environmental problems caused by our lifestyles means that we need to invent building systems that can meet these new challenges (see Section 7).

Steel is the material ‘par excellence’ when it comes to inventing new structures and forms. All solutions are possible, from the very simplest to the most challenging. Steel can be used for small buildings as well as large structures, for routine construction projects and those subject to complex urban constraints.

Figure 2.1 Energy efficient design at GLA building, London

No other material is used to make structures which are so thin, light and airy. Forms can be created using different structural effects and envelopes with pure or finely sculpted curves.

Designers can give free reign to their imagination and creativity.

Within the overall architectural concept, the structural steelwork may be concealed or exposed to reveal its essence. In both cases the advantages remain: facility for modular design, compactness, economy of material, freedom of use, speed of assembly etc.

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Figure 2.2 ING Bank Headquarters in Amsterdam

Steel provides the flexibility needed to enable a building to evolve throughout its working life. The building can be initially designed in order to facilitate future evolutions:

Modification of applied loads due to change of use of the building

Floor plan morphology in order to retain the possibility to create new openings

Horizontal and vertical movements, exits: appropriate measures can be taken in order to limit any impact on the primary building structure during alterations.

Large spans constitute one of the major benefits of steel structures, thanks to the quality of the material and the manufactured products. Large spans facilitate future developments of the structural elements. The load-bearing frame is integrated in the exterior walls of the building in order to free up space. Large spans were once confined to industrial buildings or warehouses, but are now very common in office or residential buildings.

It is advisable to adopt the principle of load-bearing columns, rather than bearing walls, in order to release the construction space from the constraints which fix a building in time and condemn its evolution. Load-bearing elements are separated from the systems which make up the envelope and the internal partitions, in order to allow future building development. Since they serve no structural function, façades, roofs and partition elements can be removed and replaced.

In multi-storey steel buildings, the vertical bracing systems must be arranged so as not to obstruct the free use of open space.

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In order to design in steel, it is essential to understand the different aspects in the construction process:

Floors

Façades

Partitions

Roofing.

Each aspect involves various products assembled in a specific order (see relevant Sections).

2.2 Prefabrication – Industrialised building systems Construction methods using prefabricated elements and components, and their adaptability in terms of new project regulations, facilitate the design and construction of buildings which are in perfect harmony with their end use.

All structural steel components are manufactured by steelmakers or fabricators using automated and computerized cutting and bending machines. Design tolerances are limited to millimetres, whilst for other construction materials they are closer to centimetres. The finished products are subject to high levels of quality control.

The components used to make a building are all prepared in the workshop and delivered ready for assembly on site. The components are not modified on site. They are ready for use.

Figure 2.3 Multi-storey industrial building during construction, in Monaco

One of the main qualities of steel structures is the speed of fabrication and erection, and of the assembly and disassembly of non permanent structures (for example, modular construction).

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Intelligent use of steel products and components produced by manufacturers who are constantly innovating and developing, contributes to the transformation of our urban landscapes.

2.3 An evolving art Today’s perception of steel has evolved. Its qualities and advantages have been revealed, tried and tested. Moreover, the very wide range of accompanying products means the steel frame can respond to rapidly changing lifestyles and use.

Many buildings constructed after the Second World War no longer fulfil today’s needs, although they can be restructured and extended if the patrimonial value of the existing building is worth prolonging.

Steel buildings are designed with walls made of light composite products. This construction solution combines all of steel’s qualities.

2.4 Extending and refurbishment 2.4.1 Extending upwards

The concept of extending buildings upwards is very interesting. The designer can benefit from the foundation of existing buildings and their vertical connections.

Load-bearing steel frames are lightweight and adaptable for many situations. They provide an effective solution for the extension of old buildings, whatever the original material, and help find the right balance between the weight of the new structure and the admissible loads.

In order to extend an existing steel structure, it is reasonable to retain the same building system.

Figure 2.4 Extending building upwards

An extension is often carried out in parallel with complete refurbishment of the building. The modus operandi for building an extension with a steel structure allows the two activities to be managed simultaneously, thus significantly reducing the time needed to refurbish the existing building. The latter can be carried out in parallel with the extension and without incurring costly delays.

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Depending on the load-bearing structure of the extension, and in the case of a reinforced concrete building whose width is not altered, the steel frame may, for the most part, be installed on the external concrete walls or columns, or even fixed to the external walls of the façades on each floor, in order to distribute the load. Both solutions avoid having to create a new structure across different levels or new foundations that are costly and difficult to build.

2.4.2 Extending width of buildings

When conditions are right for the restructuring of an existing building, the steel structure also offers an effective functional solution for extending its width.

Figure 2.5 Extension of a multi-storey building

A number of technical solutions are possible, depending on the structural characteristics of the building and the planning regulations applicable in that area:

Frames installed parallel to the building

Half portal frames supported on a parallel row of foundations separate from the building, depending on the project, and on the load-bearing structure of the building

Hangers fixed to the beams on the building super structure.

The steel structure of the extension is mechanically fixed to the building floors and load-bearing plates.

2.4.3 Conversion and refurbishment of industrial buildings

Refurbishment and conversion is estimated to account for about 50% of building work.

Structures made of steel frames lend themselves particularly well to such alterations. Many conversions involve nineteenth century buildings made of steel, such as stations, market halls and industrial workshops that are found in dense urban areas.

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It is easy to remove components, to replace and modify spans, to change beam or column dimensions. The ability to suspend building floors from roof structures offers additional flexibility for new projects associated with existing buildings.

It is also worth noting that the lightness of steel structures is a distinct advantage when adding new floors by means of connections to existing structures (once their potential has been verified). If new foundations are required for the installation of new structures, these can be designed easily and in such a way that they do not interfere with existing foundations.

The restructuring of relatively old buildings (such as that shown in Figure 2.6) always requires work to ensure compliance with current standards. It can involve:

Emergency exits

Increase in movement

Installation of ventilation and smoke ducts

Fire and corrosion protection of steel elements

Reinforcement for new loads

New means of access.

Figure 2.6 Headquarters of Nestlé France, Noisiel

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3 STEEL – MATERIAL AND PRODUCTS

3.1 Steel the material Steel offers exceptional qualities in terms of mechanical resistance. Of the most commonly used materials in construction, it demonstrates the greatest resistance for the lightest section, both in tension and compression. This opens the door for architects to a wide choice of technical and aesthetic solutions.

There are many types of steel. These are classified, according to their composition. There are three main categories of steel:

Non-alloy steel grades

Stainless steel grades

Other alloy steel grades.

Non-alloy steel grades are commonly used in the construction sector. The main steel grades are S235, S275 and S355 for structural members. However the higher strength steel S460 grade is used more and more in construction.

Steel products must demonstrate specific characteristics according to their grade and form and as defined by National or European standards.

Full information can be found on steel producers’ web sites:

www.arcelormittal.com/sections

www.corusconstruction.com

www.peiner-traeger.de

3.2 Steel products These can be classified into two main categories, as shown in Figure 3.1.

I and H sections

Channels, angles

Bars for concrete

Sheet piles

Long products (hot rolled profiles)

Coils (1,5 mm < t < 15 mm)

Plates (5 mm < t < 400 mm)

Flat products

Hollow sections

Cold formed long products

Decking, cladding, roofing

Figure 3.1 Main categories of steel products used in construction

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3.2.1 Hot rolled long products

Hot rolled long products (often referred to as ‘sections’ or ‘profiles’) are generally used for the main frame members (columns, beams, bracings).

I, H and channel sections

h

h

h

IPE 80 mm < h < 750 mm

HE 100 mm < h < 1000 mm

UPE 80 mm < h < 400 mm

Angles

h

h

Equal legs

20 mm < h < 250 mm

Unequal legs 100 mm < h < 200 mm

Hollow sections

d

t

b

t

b

t

h

Circular hollow sections 20 mm < d < 1200 mm

Square hollow sections 40 mm < b < 400 mm

Rectangular hollow sections 50 mm < h < 500 mm

Figure 3.2 Hot rolled long products used in steel construction

Sections undergo various transformations through cutting, welding, bending etc., in order to obtain very different shapes and improved performance.

In this way, cellular beams (Figure 3.3) can be fabricated from IPE or HE sections by oxy-cutting and welding.

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Figure 3.3 Cellular beams fabricated from hot rolled sections

3.2.2 Cold formed long products

Cold formed long products, formed from thin sheet steel, are generally used as secondary members for cladding (rails) and roofs (purlins).

Figure 3.4 Cold formed products – Typical sections

3.2.3 Flat products

In building construction, the use of flat products is mainly for the following purposes:

Steel decking for floors

Roofs

Cladding

For each of these purposes, thin sheet steel is used, frequently formed into profiled sheets (see Figure 3.5).

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Steel decking for floors

Steel sheeting for roofs

Steel sheeting for cladding

Figure 3.5 Use of flat products in steel construction

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4 BASIS OF GOOD DESIGN: THE STRUCTURE

4.1 The load-bearing system In multi-storey structures, load-bearing and load distribution functions are ensured by installing a main frame consisting of beams and columns.

4.1.1 Load-bearing framework

Optimisation of the number of load points is a question which is always raised at the design stage and the response must take into account the building use. As far as layout of space is concerned, columns are always considered obstacles that must be limited as much as possible. Traditional framework structures use spans of the order of 4,50 to 6 m for residential buildings. Large spans of between 12 and 18 m for offices and 15 to 16 m for car parks can free up a lot of space.

15 m 15 m

5 ×

6 m

Figure 4.1 Example of grid for columns and beams

The number of load-bearing points also depends on the type of foundation in respect of soil conditions. When the soil is poor, it is advisable to limit the foundation points and consequently reduce the number of columns. A steel frame has the benefit of reducing the overall weight of the building and therefore reducing the size of the foundations.

4.1.2 Columns

The main purpose of the columns is to transfer the vertical loads to the foundations. However a part of the horizontal actions (wind action) is also transferred through the columns. In multi-storey buildings, the columns are heavily compressed and they are designed for buckling.

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The criteria which help to determine the choice of column are usually the following:

Architectural preference

Grid layout and size

Cost of steel products (I or H sections are less expensive than hollow sections)

Installation costs (complexity of installation)

Ease and simplicity with which secondary components (for façades, walls, ceilings) can be connected

Work and products needed to respond to essential requirements (fire, corrosion, etc.).

Table 4.1 shows the main types of columns used in multi-storey buildings. Composite columns provide a better fire resistance.

Table 4.1 Main types of columns

Steel section Composite section

H-section

Circular hollow section

The column design shown in Figure 4.2 provides added value architecture, cost savings in material and optimized structural behaviour.

Figure 4.2 Building structure with tie members

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Variable profile sections can deliver a certain architectural dynamism to the design of these columns. Formed from standard sections or plates, these columns have as their main characteristic variable lengthwise dimensions which can optimize their structural function.

Since steel works equally well in tension as in compression, for functional (to avoid obstruction) or architectural reasons, a hanger or tie rod may be preferred to a column, in order to hold a beam and cross a floor space without a point of support.

Figure 4.3 Structural arrangement with hangers

4.1.3 Beams

Beams spread the vertical loads and are mainly subject to bending. The beam section must therefore present sufficient stiffness and strength in the vertical plane.

There are many different types of beam, see Table 4.2. Amongst these, composite beams are particularly well suited to multi-storey buildings. When combined with steel, the concrete works in compression and the steel (mainly) in tension: the outcome is a system that offers good mechanical performance, both in terms of resistance and stiffness.

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Table 4.2 Main types of beams

Type Comment

Rolled profiles Rolled profiles are commonly used in multi-storey buildings. A large range of dimensions and steel grades is available. Simple rolled profiles are well adapted for small and medium span ranges. Rolled profiles can be curved for architectural purposes.

Welded profiles Welded profiles are fabricated from plates. They can have flanges with different dimensions to form a mono-symmetric section. These profiles offer the possibility to design tapered members, which optimizes the quantity of material, with interesting architectural effect.

This solution is generally used for beams larger than rolled profiles.

Cellular beams By a process of oxy-cutting and welding, the cellular beams can be fabricated from rolled profiles. This is a very efficient solution for office buildings, since it offers several advantages, such as: increasing inertia compared with the basic profile, providing openings for services (ducts, air-conditioning, etc.) and architectural appearance.

Even if the openings are generally circular, other shapes are possible such as hexagonal openings.

Composite beams

When a concrete slab is supported by the beam, it is easy to ensure a structural connection between the slab and the beam. The steel profile can be a rolled profile, a welded profile or a cellular beam. The latter is especially recommended for large span floors in multi-storey buildings (up to 18 or 20 m).

Many composite beam solutions have been developed.

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Figure 4.4 Composite beam with welded studs at construction stage

Figure 4.5 Composite cellular beams with steel decking

Figure 4.6 New type of beam – AngelinaTM (composite beam), during erection

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There are several types of composite beams, as shown in Figure 4.7. In these examples, the steel profile can be a rolled profile, a welded profile or a cellular beam. In example (c), the steel profile is a rolled profile.

(a)

(b)

(c)

Plain slab: this solution requires temporary formwork.

A pre-slab or a steel decking is used as permanent formwork and contributes to the bending resistance of the slab.

The beam is partially concrete encased to improve fire resistance.

Figure 4.7 Composite beams

In multi-storey buildings, the total depth of the floors often needs to be reduced to a minimum. The design of slim floors consists of integrating the steel beam to the concrete slab. Figure 4.8 shows two types of integrated steel beams.

Figure 4.8 Integrated beams (slim floors)

Figure 4.9 shows three examples of steel beams used as integrated steel beams.

The lower flange is a plate welded to the web of a half rolled profile

The upper flange is a plate welded to the web of a half rolled profile

A plate is directly welded under the lower flange of a rolled profile

Figure 4.9 Different types of profiles used as integrated beams

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The span ranges for the various structural options for floors are shown in Table 4.3.

Table 4.3 Span ranges of various structural options

Span (m)

8 6 10 13 16 20

Reinforced concrete flat slab

Slim floor beams and deep composite slab

Integrated beams with precast slabs

Reinforced concrete beams and slab

Post-tensioned concrete flat slab

Composite beams and slab

Fabricated beams with web openings

Cellular composite beams

4.2 Bracings 4.2.1 General

A structure is statically determinate when the number of supports is just enough to ensure its global stability. By increasing the number of supports and rigid connections, the structure becomes stiffer, but rigid connections are more expensive than simple connections. So an economic compromise has to be found.

Figure 4.10shows two options for the stability in a vertical plane of a multi-storey building.

Braced structure

The global stability is ensured by cross bracing (see § 4.2.2). Simple connections are used. The bracing members in compression are generally ignored in the detailed design.

Frame effect The global stability is ensured by frame effect (see § 4.2.3) thanks to the stiffness of the connections. This solution leads to more complex connections.

Figure 4.10 Global stability in vertical planes of a multi-storey structure

The stability of a building has to be ensured in all the main planes (vertical and horizontal planes) in order to transfer the forces to the foundations, as shown in Figure 4.11.

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1 2

3 4

Key: - see text Figure 4.11 Planes of stability for a rectangular building

The vertical stability (A and C in the Figure) can be provided by any of the four systems:

1 Cross-bracing (simple construction)

2 Frame effect

3 Diaphragm effect (contribution of the cladding)

4 Concrete wall.

The horizontal stability (B and D in Figure 4.11) is generally ensured either by the diaphragm effect in concrete floors or by a cross-bracing. Horizontal stability systems must be appropriately connected to vertical stability systems in order to transfer the forces to the foundations.

Wind action is the main horizontal action in multi-storey buildings. In seismic areas, horizontal actions due to earthquakes have to be considered.

4.2.2 Braced structure option

Multi-storey buildings are generally designed with pinned members. Vertical stability is commonly provided by cross-bracing, and sometimes by a concrete core. The advantages of such a design are:

Simple connections

Quick erection

Reduced fabrication costs.

The cross-bracing can be either inside or outside the building, depending on architectural preference. An example of bracing as an architectural feature is shown in Figure 4.12.

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Figure 4.12 External cross-bracing in a multi-storey building

4.2.3 Frame effect option

In order to avoid bracing between the beams, it is possible to design rigid-jointed continuous frames.

Multi-storey buildings with a load-bearing structure formed of rigid frames often require an increase in the column section and sometimes in the beam section.

Since ensuring stability by frame action is less economical than by bracing, a combination of the two systems can provide an efficient and balanced solution. It is possible to have frames in one direction and to use bracing for stability in the perpendicular direction.

The advantages of continuous frames are:

The primary beams are stiffer – the deflections are lower than those of simply supported beams

The floors are less sensitive to vibrations

Adding redundancy to the structure increases robustness.

The disadvantages are:

The connections are more complex and the erection is more complicated

The internal forces in the columns are increased

The structure is globally more expensive.

Structures made of continuous frames in both directions are exceptional. They can be recommended for buildings with special requirements (medical research, white rooms, equipment sensitive to deflections and vibrations, etc.).

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4.3 Floors 4.3.1 General

The structural function of floors is to transfer loads to the main members of the structure. Floors also contribute to the global stability of the structure because they generally act as a diaphragm to provide stability in the horizontal plane of each storey.

The design of a floor conforms to specifications that include:

Applied loads

Thermal performance

Acoustic performance

Fire resistance

Service integration

Requirements to connect a false ceiling.

The structural part of the floor can be one of the following:

Composite slab using steel decking

Concrete slab with steel decking used as permanent formwork

Dry floors

Plain slab, concrete slab including a precast slab

Prefabricated slab.

4.3.2 Concrete slab with steel decking

The use of steel decking has many advantages:

Efficient permanent formwork (the formwork does not have to be removed after concreting)

Installation of a steel decking is easier than that of a precast slab

Propping during construction is often not necessary.

A simple steel decking is efficient as permanent formwork at the construction stage. Special steel deckings have been developed in order to contribute to the bending resistance of the floor, as a tension component. For these deckings, embossments provide a good connection with the concrete. See Figure 4.13.

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Permanent formwork (Non composite slab)

Composite slabs

(Steel deckings with embossments) Figure 4.13 Concrete slab with steel decking

To optimize structural behaviour, a composite slab with steel decking can also be designed to contribute to the bending resistance of the beams (composite beams), as shown in Figure 4.14. This leads to a reduction in the size of the steel profiles, and subsequently in the total depth of the floor, the weight of the beam, etc.

Typical dimensions of a steel decking:

Length: 6 m

Width: 1 m

Thickness: 0,75 or 1 mm.

Figure 4.14 Composite slab and composite beams

Fire resistance of slabs composed of a steel decking and concrete

The steel decking has a mechanical function of reinforcement. The underside generally requires no protection. The composite slabs can have 30 minutes’ fire resistance without special protection.

A higher resistance can easily be obtained by:

Adding reinforcement bars in the slab

Protecting the underside of the decking

Adding a false ceiling of mineral wool and plasterboard.

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4.3.3 Precast slab with in-situ topping

Plain slabs are generally composed of a precast slab and cast-in-situ concrete. At the concreting stage, temporary supports may be needed to transfer the weight of the precast slab, the concrete and operatives working on the site.

The slab can contribute to the bending resistance and stiffness of the beams if an appropriate connection (welded studs for instance) is provided between the slab and the beam – see composite beams in Table 4.3.

4.3.4 Hollow core slabs

Prefabricated hollow-core slabs are generally used with integrated floor beams (non composite beams). These elements can be placed on angles welded to the web or on the lower flange (see Figure 4.15, Figure 4.8 and Figure 4.9). A structural concrete topping with reinforcement is recommended in order to tie the units together to serve as a diaphragm component.

Figure 4.15 Hollow core slab

4.3.5 Prefabricated composite slab elements

This type of floor is manufactured in elements, the width of which is 1,20 m and the length up to 7,00 m as shown in Figure 4.16.

1

2

3

4

1 Concr ete slab

2 Steel mesh

3 Thermal and acoustic insulation

4 U-sha ped liners

Figure 4.16 Prefabricated composite slab elements

4.3.6 Dry floors

Dry floors are made of a mechanical assembly of industrialized components (see Figure 4.17). The main properties of dry floors are:

Lightness


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Thermal performance (insulation is integrated in the floor)

Speed of erection

No temporary propping during construction

Flexibility.

The transfer of the loading is ensured by the profiled steel sheeting. Its length can vary between 2,00 and 6,00 m and its depth is about 20 cm. Services (cables, ducts) can be placed in the depth of the profiled steel sheeting. An electric heating film can be incorporated in the floor.

1 Two layers of plasterboard

1

2

3

4

5

6

2 W ood board

3 Resilient material

4 Profiled steel sheeting

5 Layers of mineral wool

6 1 or 2 layers of plasterboard

Figure 4.17 Main components of a dry floor

Figure 4.18 Photo of a dry floor

The fire resistance of a dry floor depends on the fire performance of the false ceiling and the upper components made of plasterboard. Performance can be adapted to national regulation or other specific requirements.

4.3.7 Acoustic and thermal requirements for floors

In order to fulfil requirements relating to acoustic and thermal insulation, other materials can be connected to the slab. Such materials also provide an appropriate facing.

Such elements are:

Plasterboard connected under the composite floor, the number layers of which depends on the required acoustic performance

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Mineral wool layers supporting the plasterboard.

The space between the beams under the floor can be used for service integration (ducts).

Figure 4.19 Composite slab with thermal insulation

4.4 Connections 4.4.1 General

Steel construction is based on a simple principle, involving the assembly of elements, such as columns, beams, bracing members, tie members. The components of the building envelope – floors and partitions – are then connected to the principal members.

The main function of a connection is to transfer internal forces between the members, in a way that is consistent with the design assumptions – pinned or continuous connection. When the connections are visible, their aesthetic quality can emphasise the structural behaviour and contribute to the architectural value of the building

4.4.2 Types of connections

There are many types of connections for structural members. The principal types commonly used in multi-storey buildings are:

Nominally pinned connections (beam-to-beam and beam-to-column)

Moment connections (beam-to-column) for continuous frames

Connections of bracing members

Column bases.

Figure 4.20 shows three types of beam-to-column connections. These connections can be considered as pinned. This type of connection is mainly designed to transfer a shear force and a small axial force.

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End plate welded to the web of

the beam and bolted to the column flange

Fin plate welded to the column flange and bolted to the web of

the beam

Double angle web cleats:

angles bolted to the column flange and the beam web

Figure 4.20 Typical beam-to-column connections – pinned connections

Figure 4.21 shows the connection of a secondary beam to a primary beam using double angle web cleats. The secondary beam is notched so that its top flange is at the same level as the top flange of the primary beam.

Figure 4.21: Typical beam-to-beam connection

Figure 4.22 shows an example of rigid beam-to-column connection. The end plate is welded to the beam and bolted to the column flange. This type of connection is designed to transfer a bending moment and a shear force.

Figure 4.22 Moment connection

In multi-storey buildings, the column bases are generally nominally pinned, such as that shown in Figure 4.23(a). Significant compression force is

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transferred to the concrete foundation. In routine situations, the shear force remains quite low. Figure 4.23(b) is a fixed column base, shown here by way of comparison.

(a) Pinned column base

(b) Fixed column base

Figure 4.23 Column bases

The ends of bracing members are usually bolted onto gusset plates. The gusset plates can be bolted, or sometimes welded, to the main members (beam and column). An example is shown in Figure 4.24

Figure 4.24 Typical connection of a bracing member

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4.5 Summary Table 4.4 gives typical weights of building elements.

Table 4.4 Typical weights for building elements

Element Typical weight

Precast units (spanning 6 m, designed for a 5 kN/m2 imposed load)

3 to 4,5 kN/m2

5 kN/m2 Plain slab (Normal weight concrete, 200 mm thick)

2,6 to 3,2 kN/m2 Composite slab (Normal weight concrete, 130 mm thick)

2,1 to 2,5 kN/m2 Composite slab (Lightweight concrete, 130 mm thick)

0,25 kN/m2 Services

0,1 kN/m2 Ceilings

35 to 50 kg/m2 Steelwork (low rise 2 to 6 storeys)

40 to 70 kg/m2 Steelwork (medium rise 7 to 12 storeys)

Steel provides many advantages to the architect for the design of a multi-storey building:

Large spans are possible

A steel building is lighter than a traditional building

The foundations are simple and less expensive

This solution is well adapted to soils with poor load-bearing qualities.

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5 BASIS OF GOOD DESIGN: THE ENVELOPE

5.1 Façades 5.1.1 General remarks

When steel is the material of choice for construction, façades are made up of a series of fabricated products which fulfil the following functions: load-bearing capacity, air tightness, water tightness, protection against intrusion, thermal and acoustic insulation, fire protection and, of course, aesthetic appearance.

Application of these products for façade systems guarantees a high level of precision and performance and therefore demands a certain degree of design rigour, particularly in the connection and cladding details of the various components.

With its component elements, the steel in a façade can be used for secondary frames (light steel elements or double skin façade with steel sheeting or trays), support for external facing, cladding and, lastly, for decoration and solar protection.

Steel construction solutions can also be combined with other types of façade facing: steel cladding, stone, brick, terracotta, wood and glass (see examples in Figure 5.1). They offer a true palette of architectural solutions in terms of appearance, shape and finish.

The huge range of façade dressings can influence performance and provide solutions for all types of project (Figure 5.2), including:

Public amenities

Offices

Apartments and hotels

Commercial buildings.

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Steel cladding – Montargis (France)

Steel cladding – Montargis (France)

Terra Cotta – Fulham (United Kingdom)

Stone – Bagnolet (France)

Wood– Luxembourg (Luxembourg)

Render on load-bearing walls – Helsinki (Finland)

Figure 5.1 Types of material for façades

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Millenaris – Budapest (Hungary)

European Parliament (France)

House buildings - Evreux (France)

University – Torino (Italy)

Figure 5.2 Façades for various types of project

5.1.2 Positioning the façade

There are three configurations for positioning the façade in relation to the structure, as shown in Figure 5.3.

EXTERNAL: curtain wall, prefabricated wall panels

DOUBLE FAÇADE: infill light walls and external cladding INTERNAL: panel walls façade

Spinningfield office

Manchester Royal northern college of music

Manchester Industrial workshops for public transportation company - Paris

Figure 5.3 Positioning the façade

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The features of these three options are:

A completely external façade: the structure is visible inside

- The façade is a series of panels installed between floors

- If the column is hidden, the most cost efficient section should be used

- If the column is visible, the aesthetic appearance will need to be considered.

- In this case, fire protection requirements vary according to the building use and there are numerous solutions to satisfy these (see 6.2.4).

A double façade thickness:

- Generally speaking, and since the column is not visible, the most economic solution will be determined by the choice of section.

- If sizing leads to a discontinuity in the façade facing, the columns can be divided into two in order to reduce obstruction.

- Internal and external facings which have been adapted will ensure structural fire protection.

Internal façade: the structure is visible outside the building

- The façade beam connection must be examined carefully, especially in terms of thermal, structural and fire protection needs. Special arrangements can be put in place.

5.1.3 The construction principle

In most construction elements for lightweight façades, the edge of the floor is used to determine the limit. The vertical plane it defines is for fixing elements, for reducing thermal bridging and for fire protection between floor levels.

On the outside, are the support elements for the external facing (secondary frames, plates), which are installed vertically or sometimes horizontally. A primary layer of thermal insulation is then applied. The external facing is placed on this frame using a fixing device (transverse frame, bracing, pre-frame, etc.). The external facing can be fabricated panels with insulation (Figure 5.4).

On the inside, a double-skinned partition, comprising between one and three layers of plasterboard fixed to a light steel frame, is commonly used. Additional insulation is applied between the frame posts (Figure 5.5).

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Pre-fabricated large wall panel with integral SHS sections (Finland) Example of Vertical cladding

1 Internal cladding – support for the façade 2 Thermal or acoustic insulation (1st layer) 3 Thermal insulation – 2nd layer behind steel trays 4 External cladding

Figure 5.4 Cladding

Figure 5.5 Thermal insulation

These lightweight façade systems often contain an air space for ventilation between the continuous insulation layer applied in front of the floor edge and the internal side of the outer facing.

This arrangement is conducive to good hygrothermal performance of the partition wall and facilitates installation of unjointed facing elements. However, installation of a rain screen to protect the external insulation layer is essential.

If the external facing is watertight, the air space cannot be introduced and the façade will not be ventilated.

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Detail for bottom of infill walls Detail for top of infill walls

A Slab 1 Gypsum board 5 Screw B Frame axis 2 Light steel gauge rail 6 Steel frame C Ventilated air layer 3 Light steel gauge post 7 Air barrier D Internal side of external skin 4 Hole for services 8 Joint treatment Figure 5.6 Infill walls

5.1.4 Thermal and acoustic elements

Thanks to the two insulation layers, it is possible to vary the type (mineral wool, polyurethane, cellular glass) and the thickness of materials used and thus to eliminate a substantial amount of thermal bridging. The risk of direct heat transfer (cold bridging) must be treated at the level of the fixings and joints between the metal parts which are in contact with internal spaces and external areas.

Acoustic performance also depends on the system and fixing of the external cladding and the insulation density. To improve comfort, the internal finish facing material can also consist of perforated metal sheets (see Figure 5.4), allowing the mineral wool insulation material in the façade to correct the acoustic performance through atmospheric absorption at a high sound pressure level.

Lightweight façade solutions using steel structures are ideally suited to new construction and also to refurbishment and in particular to upward building extensions.

University of technology, Rzeszow (Poland) Residential building (Denmark)

Figure 5.7 Refurbishment and extensions

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Table 5.1 Comparative weights of façades and partitions

Type of façade Weight (kg/m2)

Heavy façade: - Bearing wall of 18 cm - 8 cm outside insulation - Terracotta or stone facing 20 to 50 cm

80-100 (wall not included)

Light façade: - Secondary frame of façade (cold-formed profiles) - A layer of mineral wool - Partition of dubbing of 0,07 cm - Outside finish facing - steel tray

30-50

Concrete wall of 20 cm 500

2 H-shaped columns of 0,20 m 1 I-shaped beam of 0,27 m Light partitions of 0,20 m

30-50 depending on the use

5.2 Roofing systems 5.2.1 General remarks

Steel frames can accommodate all types of roofs, from watertight roofs to flat or arched roofs, as well as opaque or glass roofs.

SuperC building – Aachen Stone – Bagnolet

Wood– Luxembourg Pitched roof on site Glass roof

Figure 5.8 Roofs

The building envelope needs to respond to many different requirements, see Figure 5.9.

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WIND

SNOW, Maintenance

WIND

Watertightness Pressure and depression External and internal hygrometry Durability Accessibility and maintenance

Figure 5.9 Requirements for building envelope

Roof typology depends on several criteria, including shape, roof slope, external appearance, material colour, type of support and the materials used.

Roofs are usually divided into three types:

Flat roofs with no slope

Pitched roofs (slope between 3 and 7%)

Steep or arched roofs

‘T’ Intersection roof with gable side

Overlaid Hip roof with gable side

Hipped roof Flat roof

Figure 5.10 Roofs

For low slope roofs, the most important elements for the steel frame are the quality of fixings and arrangements for rainwater evacuation (Figure 5.11).

5.2.2 Flat roofs

The principle of flat roofing systems on surface support elements can be applied using lightweight partitions, a metal sheet (see Figure 5.12) or the concrete topping technique with a concrete compression decking.

A vapour screen, thermal insulation and waterproofing, with or without protection, are installed on the upper side. In order to provide the parapet which will be used to increase water tightness, it is possible to use a secondary steelwork façade which can be en extended to the required height.

5.2.3 Pitched roofs

In the case of a low pitch roof (slope between 3 and 7%), water tightness is also obtained by applying bituminous products or PVC watertight membranes. Insulation is applied directly to the galvanized steel sheet tray. The process is light and economical for non-accessible roofs. Phonic insulation is adjusted through thickness of the materials and the order in which these are superimposed.

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Fixing on steel purlins with self-drilling or self-tapping screw

Fixing on wood purlins

1

Screw hook

1 Fixing without cover piece Figure 5.11 Types of fixings

1 Seal ant coating

4

1

3

2

5

6

2 Rigi d insulation 3 Insulati on connection 4 Steel sheet 5 Scre w on beam 6 Beam

Figure 5.12 Typical view of a flat roof

Figure 5.13 Corner of façade and roof – On site view

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5.2.4 Steep or arched roofs

Water tightness is easily obtained by overlapping of the metal sheets, more or less following the roof slope and the product. The most common procedure is to superimpose materials so that all air space is eliminated.

Figure 5.14 Curved roof

5.2.5 Roof construction

A typical roof construction, from the exterior inwards, consists of:

A ribbed steel decking fixed perpendicular to the panels

A primary layer of insulation made of a taut felt sheet combined with an internal vapour screen placed between the decking and panels

A second and thicker layer of mineral wool

A steel frame on which to fix the product which is used for the internal finish

A second vapour screen

An internal finish facing material, of one or two layers of plasterboard screwed to the steel frame or, in some cases, steel decking or perforated steel decking.

Acoustic insulation to control rain noise is particularly effective.

Roof netting systems with different amounts of perforation can be fixed on metal roofs to handle thermal shock and to improve the architectural concept using a canopy.

Galvanized steel sheets, whether pre-painted or not, and stainless sheets, are particularly suitable for arched roofs (see Figure 5.15). Stiffening ribs improve bending strength.

The plates are supported by panels, the characteristics of which determine the spacing and loads to be carried. Fixing is carried out above the stiffening ribs, using compressed watertight joints.

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Figure 5.15 Curved roof with galvanized steel sheet

5.2.6 Renewable energy systems

The roof can be designed to accommodate various systems for renewable energy, such as solar panels. Figure 5.16 shows photovoltaic panels on a residential building.

© SYSTAIC

Figure 5.16 Photovoltaic panels installed on a roof

Figure 5.17 shows wind turbines with vertical axis installed on a flat roof.

www.innoenergie.com

Figure 5.17 Array of small-scale vertical axis wind turbines on a flat roof

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http://www.innoenergie.com/


6 OTHER FACTORS FOR GOOD DESIGN

In addition to the benefits described in previous Sections, which were concerned with mechanical performance and technical application, steel offers:

Savings in structural weight

Optimized space and return on investment

Clean and efficient construction sites.

Good practice in steel building design and the appropriate choice of materials, mean all the following requirements can be met, whether regulatory or at the client’s request:

Seismic behaviour

Fire resistance


Thermal performance

Sustainability

Service integration.

6.1 Behaviour during an earthquake Steel structures are particularly well suited to construction in earthquake zones. This is mainly due to reduced accelerated mass, as well as the high ductility of steel material that allows significant energy dissipation.

Good seismic performance of steel structures is demonstrated by the fact that destruction of steel buildings due to earthquakes in any part of the world is rare. The most recent analysis of the consequences of a major earthquake in Europe confirms this fact. On April 6, 2009, a magnitude 6.3 earthquake struck close to the city of L’Aquila, located approximately 90 km north-east of Rome. Steel structures in the region affected by the earthquake were mainly industrial or commercial buildings, located outside towns. These structures suffered very little damage. Any minor damage recorded did not affect their structural integrity and there was a rapid resumption of activity. The photographs in Figure 6.1, taken in the days that followed the earthquake, show the commercial centre of Aquilone.

It is worth highlighting that the centre for emergency relief was set up in the gymnasium of L’Aquila. This steel building, which consists of circular columns and a three-dimensional truss roof, provided a huge empty space and it was possible to continue to use it despite the many aftershocks in the weeks following the main earthquake. The Italian authorities have every confidence in the seismic behaviour of this type of building.

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Figure 6.1 Commercial centre of Aquilone

6.2 Behaviour during a fire 6.2.1 General remarks

Requirements in terms of structural behaviour during a fire are defined in national regulations. These depend on the end-use of the building, its size and accessibility, and the consequences in the event of collapse.

The objectives of fire safety objectives are:

To ensure stability of the load-bearing elements for a specified period of time

To limit the emergence and spread of fire and smoke

To facilitate rescue operations

To facilitate safe and rapid evacuation of occupants

To limit the spread of fire to neighbouring structures.

To achieve these objectives, regulations impose different types of requirement:

Requirements relating to materials: reaction to fire

Requirements for building elements (principal structural and secondary non-structural elements): fire resistance, enhanced by passive protection

Requirements related to layout of access and measures for active protection.

It is essential to take account of these requirements from the initial stages of design. To consider fire protection requirements as an afterthought could result in significant costs or even call into question the actual design.

6.2.2 Reaction to fire

Certain materials can speed up the development of fire. Table 6.1 gives the European classifications for reaction to fire of building materials. Steel, a non-combustible material, is classified as A1.

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Table 6.1 European classification for building materials

Class Comment

A1 non-combustible products No contribution, even in highly developed fire. Must automatically satisfy other less stringent classes

A2 non-combustible and not very combustible products

Class B + little contribution to fire load and to development of fire in event of very developed fire

B combustible products Item C with even stricter criteria C combustible products Item D with stricter criteria D combustible products Product resisting attack of small flame for longer period.

Capable of undergoing thermal attack from isolated object on fire with delayed and limited heat release

E combustible products Products capable of resisting attack by small flame without substantial spread

F unclassified products No fire reaction performance defined

The system provides additional classifications, as given in Table 6.2.

Table 6.2 Additional classes

Production of inflamed smoke Production of droplets or debris

S1 low smoke production d0 absence of inflamed droplets S2 medium smoke production d1 no inflamed droplets exceeding 10 seconds S3 no limit required d2 inflamed droplets (persistence > 10 seconds)

6.2.3 Fire resistance

Resistance to fire is the ability of a building element to continue to perform its intended function in fire.

The fire resistance classification of a building element is defined by:

Standardized criteria (see Table 6.3)

Degree of fire resistance (duration, expressed in minutes, before reaching criteria)

It measures the fire performance of the classified element.

Requirements for fire resistance of building elements are expressed in terms of a classification criterion and a time for which the criterion must be satisfied.

Table 6.3 Classification for building elements

Criteria Definitions

Mechanical resistance: ability to resist thermal attack from fire without loss of structural stability

R

Air tightness in a fire: ability to prevent spread of flames and hot gases E Thermal insulation: ability to prevent increase in temperature of side not exposed to fire I Thermal radiation: ability not to emit thermal radiation greater than 15 kW/m² W

The classification of a construction element may be:

R, RE, E, REI or EI, followed by the time in minutes -15, 30, 60, 90, 120 minutes, etc.

Additional criteria and criteria specific to certain facilities are also given - see Table 6.4.

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Table 6.4 Additional and specific criteria

Criteria Additional criteria

Air tightness to cold smoke: Prevents propagation of smoke in fire, even if relatively cold

S

Automatic shut down: Door, valve or shutter closes automatically C

Resistance to impact: Vertical partition to resist lateral mechanical shock M

Criteria Specific criteria

Outlet ducts for smoke (30 min): Outlet duct removes hot gases during the first 30 minutes

B0

Barriers (30 min): Confine hot gases and smoke during initial 30 minutes D Smoke vents (30 min): Remove hot gases and smoke during initial 30 minutes F

Tests or calculations are needed to demonstrate or justify the fire performance of a building element or product. Tests are defined by standards which define the methods and experiments to be undertaken for a specific type of behaviour.

Calculations can be based on conventional approaches (constant increase in temperature over time), or on the new approach to fire safety engineering introduced by the Eurocodes, through advances in knowledge about the behaviour and development of fire.

6.2.4 Passive fire protection methods

As with other materials, the strength and stiffness of steel decrease at elevated temperatures.

Conventional fire resistance of an unprotected steel section rarely exceeds 30 minutes when subjected to normal levels of loading.

Passive fire protection is therefore used to slow down the heating of steel structures in order to give the required fire resistance.

A number of systems are available: these are listed below. They provide the steel structure with the appropriate levels of protection, regardless of building end-use. They are sometimes combined.

Screen protection

Screen protection isolates the structure from an advancing fire by the interposition of elements that form a continuous wall. In a vertical position they serve as wall panels; when horizontal, they are suspended ceilings. All products used must have been tested for fire resistance.

The screen should be chosen for its fire resistance properties and can be used for acoustic and thermal insulation, as well as for aesthetic reasons.

Spray applied fire protection This is the most common form of protection. There are two basic sorts of product, thick film and thin film.

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Figure 6.2 Fire protection

With thick film coatings, the spray product or coating is fibrous or paste-like. It is generally composed of mineral fibres, vermiculite, slag or gypsum, together with a binder. It is sprayed on with special equipment under wet conditions. Several layers may be necessary, which increases the drying time.

Fire protection can last up to 4 hours.

Thin film coatings, called intumescent coatings, have a special property - they swell heat. When cold, the film thickness is between 0.5 and 4 mm. When heated to a temperature between 100° C and 200° C, the film swells and turns into foam, reaching thicknesses of 30 to 40 mm; this protects the steel element.

These paints are applied with a spray or brush and careful application of the products ensures that protection is uniform.

Conserving the aesthetic appearance of the steel is the main advantage in this type of protection, which can last up to 120 minutes.

Board protection

Board protection is achieved by forming a casing around the steel element. This is done with mechanical fasteners (screws, staples) or adhesive. The boards are made of gypsum, vermiculite, mineral fibre or calcium silicate compounds.

The principle consists in.

The passage of hot gases into the joints is a risk and requires special attention during application. This solution must be very carefully applied.

Performance may reach R120.

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Composite steel-concrete construction

In composite construction, the combined properties of steel and concrete can increase the fire resistance to cold and fire.

Figure 6.3 Composite construction

For I or H columns, the composite section consists of a complete coating, or more often a filling, between the web and flange, as shown here.

For tubular columns, the section is rendered composite by filling the tube with concrete.

The weight of the columns is significantly increased, but the performance can achieve a resistance of R180. Composite steel-concrete design is also effective in providing the floor beams with significant fire resistance.

Placing structure outside the envelope An external structure is only exposed to flames projecting from openings and from burning parts of the building. Contact with the ambient air also helps to cool it down.

Positioning the structure outside the building can avoid the need for fire protection.

6.2.5 Active fire protection methods

When dynamic fire protection devices are used (detection, alarms, smoke extraction, sprinklers) or if there is human intervention to put out the start of a fire (extinguishers), these are called ‘active’ methods.

Smoke detection Signs Smoke extraction extinguishers Sprinklers Figure 6.4 Active fire protection methods

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Their main purpose is to limit the spread of fire, in order to allow people to escape as quickly as possible and to facilitate the prompt intervention of the emergency services.

Detection systems

Fire detection requires different types of devices that are characterised by the processes they use (static, velocimetric or differential), the phenomena detected (smoke, flames, heat, gas) and the sphere of activity (confined or linear).

Table 6.5 Main type of detectors

Detectors Function Application domain

Ionic Comparison between ambient air and air contained in exposed room

Offices, circulation areas

Smoke Abatement or diffusion of light through smoke

Computing areas or areas prone to smoke

Flames Optical system, sensitive to infrared or ultraviolet light)

Storage of inflammable liquids or electrogen group

Thermal Sensitive to heat Aggressive areas (in combination with other forms of protection)

Thermal velocimetric

Sensitive to rapid increase in temperature

Aggressive areas (installation near sources of normal heat)

Autonomous Detection and Release systems (ADR) also exist. After detecting a local phenomenon linked to fire, one or more Activated Safety Devices (ASD) are released; the purpose is to activate the safety equipment: fire door, smoke extractor, etc.

Extinguishers and smoke extraction systems

Extinguishing systems commonly applied in warehouses create a foam blanket, the effect of which is to reduce oxygen and/or to cool down the premises.

Automatic water fire extinguishers (sprinklers) are designed to detect fire by means of thermo-sensitive sprinkler heads.

Gas extinguishers using CO2, FM200, Novec or other gases which rely on the principle of CO2 reduction in the area subject to fire. This process is often used in computer offices, white rooms/laboratories or hospital theatres), etc.

Outlet ducts are used to evacuate smoke and hot gases in order to allow people to escape and to limit increase in temperature of the premises. These come in various types of openings (single or double doors with intumescent strips), which are placed on the roof or façades and can be released manually with fuses or using an ADR.

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Figure 6.5 Smoke extractor

6.2.6 Other requirements

National regulations also define requirements for:

Facilitating evacuation of occupants (number and size of exits)

Protection of individuals (containment of fire, confinement of smoke and smoke evacuation, emergency exits, legibility of escape routes, duration of building stability for evacuation purposes)

Response by emergency services (access to building, safety standards, training).

6.3 Acoustic performance 6.3.1 General remarks

In order to ensure an acceptable degree of acoustic comfort, national regulations draw up requirements in accordance with building end-use.

The occupants of a building must be protected from different noises:

Airborne noise: vibrations which begin in the air.

This is the sound of voices or internal and airborne ambient noise, or road traffic as external airborne noise

Structure-borne noise: resulting from shock and solid-borne vibrations.

These are the sounds of footsteps, fallen objects, impact.

Noise from equipment: generated by the operation of equipment, these are air-borne vibrations emitted through their media.

These are the sounds of ventilation, heating, sanitary appliances.

The transmission of noise from the outside to a room, or from one room to another, occurs through vibration. This can be distinguished as:

Direct transmission: through the wall which separates the receiving from the originating area.

Lateral transfer: through the walls which are connected to the partitioning wall

Parasitic transmissions: these result from single points in the partition wall (air intakes, ducts or installation defects).

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Acoustic insulation provided by a partition lies in its ability to resist the transmission of sound from one side to the other. The sound reduction index is used to measure the performance of the wall. This is expressed in dB.

Regulations set minimum values for this index as a function of the building end-use, of the type of facilities being separated and for the airborne sound, impact sound and equipment noise.

It should be noted that the insulation provided by a real wall is always less than the index measured in the laboratory, because of lateral transfer and parasitic resonance.

The acoustic behaviour of a wall is illustrated by applying the mass-spring-mass law:

The acoustic reduction index increases with the surface density of the wall

For a double skin wall (two sandwich panels), this index depends on:

- Mass per unit area of each partition

- Thickness of the air space between partitions

- Thickness of acoustic absorption

- Critical frequency of each partition

The index of a double skin wall is much greater than a single wall with the same surface density. (The sound emitted from a room and spreading to another room horizontally and vertically passes through first layer of products which causes an initial reduction. It is then ‘trapped’ in the central void of the wall, where it bounces against the second partition and is absorbed by the insulation layer before returning residually through the second partition wall).

The acoustic performance of a steel building depends on the composition of the various partitions: external and internal, vertical and horizontal. Construction solutions are available which can achieve the very highest levels of performance.

6.3.2 Partitioning

Partitioning usually consists of thin, cold formed steel elements on which plasterboard sheets of varying thicknesses are screwed onto both sides. This creates a central air cavity in which one or more layers of insulating mineral wool are inserted.

It can incorporate the main structural building elements.

The composition of a partition wall can be adapted to the required level of performance by varying the following parameters:

Thickness of the air cavity: the more this increases, the higher the acoustic performance; the size of the main structural elements governs the choice of thickness

Composition of each facing (number and type of plates finished in plaster)

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Partition frame: use of a double metal stud wall separate from the building improves performance

Absorbent pad: the type and thickness of the insulation affects its quality.

21

3

4

5

7

6

8

Installation of a resilient joint under the panel rail of

each frame is strongly recommended.

1 Angle 5 Plaster board 2 Seal 6 Rail (70 mm) 3 Mineral wool 7 Air-tightness seal 4 Upright 70 (independent double frame) 8 Closed cells moss

Figure 6.6 Double skin partition

6.3.3 Floors

In steel framed multi-storey buildings, the composition of the floors is completed with the installation of steel sheeted plasterboard to improve acoustic performance. This can be adapted for all types of floors: concrete decks, cellular structures, composite floors, etc.

Several parameters influence acoustic performance:

Thickness of the concrete deck

Depth of the ceiling void under the slab (minimum 60 mm, maximum 100 mm)

Type and number of plasterboard sheets (1 or 2 standard or special sheets)

Type of absorbent mattress placed between the false ceiling and the slab.

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1

3

5

6

4 1

2

(plaster board + mineral wool)

1 2

3 4

1 Plaster board 4 Mineral wool 2 Steel sheet 5 Rail 70 mm 3 Plaster board 6 Fixing

1 Resilient strips under rail 2 Gap if slab depth < 15 cm 3 Ceiling void interrupted by the

partition 4 Seal

Figure 6.7 Cross sections on floor

Particular attention should be paid to the control of horizontal transmission:

Depending on the thickness of the slab, it may be necessary to make a cut in the slab perpendicular to the partition walls.

For the same reason, the ceiling void formed above the false ceiling must be interrupted perpendicular to the partition walls.

Finally, at the bottom of the walls, holes for technical equipment must not be drilled opposite one another (minimum spacing of 50 cm)

Figure 6.8 On site supplies with installation of plasterboards – Partitions and

ceilings

6.3.4 Light façades: Curtain wall systems

The acoustic performance of curtain wall systems which usually make up the steel building envelope is obtained through construction similar to that of internal partitions:

External cladding

Internal facing

Air cavity with a filling of an absorbent mattress (mineral wool).

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The careful application of all these façade components is a pre-requisite to ensuring a satisfactory efficiency.

NO

YES

At the intersection with the wall, these facings must be separated by the partition wall. Likewise, vertically, the internal facings of the lining continue as far as the decking, by stopping the suspended ceiling

Figure 6.9 Horizontal cross section at the junction between façade and

partition

6.3.5 Steel roofing systems

There are special techniques for treatment of metal roofing (film or spraying) in order to reduce the noise of impact caused by rain.

6.4 Thermal performance In order to guarantee an acceptable level of thermal comfort for the occupants of buildings with controlled energy consumption, national regulations determine the material requirements for thermal performance. These depend on the building end-use and location.

The requirements can be defined in terms of:

Restrictions on energy consumption needed for thermal comfort

Restrictions on indoor temperature during the summer

Minimum thermal characteristics of envelope and equipment (restricting heat loss – effect of thermal bridging).

Section 6.3 dealt with different ways of conforming with regulatory requirements for the acoustic performance of steel buildings. The provisions do for the various partitions typically use mineral wool as a mattress in the composite walls and its presence in the walls that surround the rooms also protects them from heat loss.

Between two floors, for example, calorific loss is reduced because layers of mineral wool are used in the composition of the floors (above and below).

Separating the two layers of insulation means that the type and thickness of the materials can be varied, thereby eliminating a large amount of thermal bridging.

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Insulation materials include rock wool or glass, polyurethane foam and polystyrene foam.

The risk of direct temperature transfer between the metal parts in contact with the outside and the inside areas of the wall must be dealt with at the level of the fittings and joints.

6.5 Durability of steel structures This Section covers the durability of steel building components. Sustainability of the material itself, particularly in respect of recycling, is discussed in Section 7 of this document.

Damage to a steel construction component arises mainly from two phenomena: fatigue and corrosion. Routine multi-storey buildings covered in this document are not affected by fatigue. This Section is therefore concerned only with the corrosion.

It is important to note at the outset that the steel frame buildings do not generally suffer major damage as a result of atmospheric corrosion. Moreover corrosion is not an issue for internal steelwork.

Even if, in the absence of adequate protection, structural elements subjected to normal atmospheric conditions may rust on the surface, this phenomenon is rarely the cause of damage to buildings, as long as a few elementary precautions are taken.

In contrast, the atmospheric conditions in some regions, such as coastal areas with a saline climate, or where there are industries that give rise to corrosive vapours, may result in steel structures having to be protected and maintained.

6.5.1 The phenomenon of corrosion

Corrosion is caused by the formation of metal salts on the surface of the steel component when a metal is combined with other elements. For example, iron corrosion leads to the production of iron oxide.

The corrosion process may be:

Chemical: through reaction between the metal and a gas phase or liquid.

Electrochemical: formation by electric current and oxidation of the anode.

Biochemical: by attacking bacteria.

Steel corrosion

Rust is the result of steel corrosion and is mainly composed of iron oxides and hydroxides, which grow in the presence of moisture and oxygen content in the atmosphere.

The oxide layers are generally non-adherent and oxidation spreads steadily. The parts lose weight linearly as a function of time.

The corrosion product does not protect the steel.

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Atmosphere and climate are parameters that have a significant influence on the aggressiveness of corrosion.

Atmosphere

The general atmospheric conditions at the building location affect the rate of corrosion: there are four general conditions:

Rural: alternation of wet and dry atmosphere – absence of pollutants

Urban: alternation of wet and dry conditions – present of sulphur dioxide (SO2)

Marine: high relative humidity – presence of chlorides which accelerate corrosion.

Industrial: presence of chemical agents – aggressive corrosion linked to degree and rate of pollutants

Climate

Heat and humidity are factors which accelerate the phenomenon of corrosion. In tropical climates, aggressive corrosion in rural environments is comparable with that in large industrial areas in temperate climates.

Some elementary precautions

In steel construction design, every means of limiting the effects of corrosion should be adopted:

Avoid creating areas of moisture and water retention for elements which are exposed to weather

Avoid contact between materials which have different electro-chemical potentials (e.g. aluminium and unprotected steel).

Protection of steel construction elements

It is advisable to adapt the degree of protection to the conditions in which the steel construction elements are installed.

There are two main forms of protection:

Painting

Galvanizing.

6.5.2 Paint protection

Table 6.6 summarizes common coating systems for corrosion protection.

It is worth noting that steel structures located inside a building where the atmospheric conditions are neither wet nor aggressive, and are permanently protected from the weather, would not suffer corrosion to the extent that it affects their resistance, even if they were not protected. However, what cannot be excluded is the unattractive appearance of rust: this can be prevented by applying a light paint coating.

Surfaces which remain unprotected must be visible in order to detect any unexpected degree of corrosion.

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Table 6.6 Protection and thickness of coating

Conditions of use Traditional anti-rust coating Coated steel products

Elements incorporated in floors and façades, protected in absence of humidity

1 or 2 primer layers of anti-rust paint, 40 to 50 microns thick

Lacquered and painted products: 15-20 microns thick

Elements inside buildings without constant humidity

1 primer of anti-rust paint, 1 paint finish, 60 to 80 microns thick

Lacquered and painted products. 1 paint finish. 60 microns thick

Elements inside unheated buildings or where humidity is high

2 primers of anti-rust paint. 1 intermediate layer of paint, 1 finish of paint, 80 to120 microns thick

Lacquered and painted products: 1 to 2 finishes of paint 80 to100 microns thick or Galvanized or pre-lacquered products

Elements in contact with aggressive external atmosphere, humid climate, urban or industrial regions

2 primer layers of anti-rust paint, 1 intermediary layer of anti-rust paint, 1 finish of anti-rust paint, 120 to 200 microns thick

Lacquered and painted products + 2 finishes of paint 100-120 microns thick Or: Galvanized or pre-lacquered products

Elements in contact with marine environment

2 primers of anti-rust paint or galvanizing/metalizing with 1 layer of zinc 1 intermediary layer of anti-rust paint, 1 paint finish, more than 150 microns thick

Lacquered or painted products+ 2 layers of paint with high content of zinc or Galvanizing or metalizing + paint with high content of zinc Or: Pre-lacquered products

The steel elements are usually delivered to site with a surface coating consisting of an anti-rust primer. Once the elements are installed, it is necessary to touch up any coating which has deteriorated during assembly.

Although elements embedded in concrete are generally not painted, those parts which are not fully covered by concrete are often prone to corrosion and must be carefully protected (including column ends).

For those parts of the elements concerned, the welds are performed and checked before applying surface protection. The welding procedure must be adapted for pre-painted products.

Estimated life of paint protection: 8 to 10 years to first maintenance

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6.5.3 Protection by galvanizing

The principle of galvanizing is the formation of protective layer of zinc and zinc-steel alloy on the surface of the steel parts in order to protect against corrosion.

The galvanized layer which is gradually oxidized to form corrosion products that are generally adhesive.

However, this form of protection is time limited and loses its effectiveness when all of the zinc coating has corroded.

Speed of corrosion and life of protection

Atmospheric conditions and climate have a direct impact on the rate of corrosion. Polluted industrial conditions near the sea are obviously more aggressive than the rural hinterland.

Depending on atmospheric conditions, the corrosion rate varies between 0,1 microns/year and 8 microns/year.

EN ISO 14713[1] provides guidance on the average annual zinc corrosion rate. This allows lifetimes to be estimated according to the coating thickness.

Estimated life of protection by galvanizing: approximately 25 years

Aesthetic appearance and painting

All galvanized steel can be painted to alter the surface appearance. Painting greatly enhances the life of the galvanized steel. Maintenance painting of galvanized steel is very easy: a brush is used to apply new layer of paint to the damaged area. The paint can also be applied as an additional form of corrosion protection in environments where acidic solutions may attack the surface coating.

Galvanizing processes

Zinc can be applied either by immersion or spraying (metalizing solution) or by electrolysis. Immersion is generally used for new parts, for dimensions compatible with the size of the baths. Spraying is used instead for renovation work or for larger building elements. Electrolysis is suitable for small parts and batch processing (e.g. bolts).

Some observations

Welding: Before welding galvanized parts, it is recommended that the coating is removed in the area of the weld seam. After sealing, the affected area will be protected by a zinc-rich paint.

Exposure to fire: A galvanized steel part that is exposed to fire behaves like uncoated steel and there is no improvement in fire resistance.

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6.6 Service integration 6.6.1 General remarks

A multi-story building, regardless of end use, is the combination of multiple elements or sub-elements that contribute to its performance: not only the structure and envelope, but also the technical installations and services which sustain the life of the building.

The control of interactions between the services and the building structure should allow:

Ease of access to services for maintenance purposes

Facility to replace elements where their life span is shorter than the structure

Prevention of nuisances arising from vibration of structures due to operation of equipment.

The main services to be installed are:

Heating and air conditioning,

Ventilation,

High and low current power supplies.

Services to the whole building are supplied using horizontal and vertical systems.

6.6.2 Horizontal systems

The steel structure and envelope offer very efficient methods of service integration using horizontal systems, as illustrated in Table 6.7. It is worth highlighting the use of cellular beams in this context (see sections 3 and 4 in this document for a description of these products). Since services can pass directly through these beams, the floor-to-floor height can be reduced. In some cases, this allows another floor to be added without altering the overall height of the building.

The standard configuration of cellular beams (regularly spaced cells of the same size) can generally be adapted to create larger openings, especially near the mid-span, in order to allow the passage of large rectangular ducts (Figure 6.10).

6.6.3 Vertical systems

Steel construction and standard envelope systems also offer flexible integration of vertical systems, due to open spaces in the wall thickness.

Achieving floor openings, and changing their location during the life of the building, is facilitated by the use of composite dry floors.

It is best to prevent the passage of services through hollow sections (between flange plates) because of potential problems with beam/column connections and in event of application of fire protection coating.

The integration of vertical pipes in tubular columns is not recommended because of lack of access for maintenance.

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Table 6.7 Integration methods for horizontal systems

Sytem Feature

Visible systems For economical, technical or architectural reasons, services can remain visible. The advantage lies in access to services, while the disadvantage is the risk of shock on unprotected pipes.

Above ceiling systems Services can be installed above floors then concealed by false open or closed ceilings and can be fully or partially dismantled. The ceiling void is cut alongside the acoustic partitions, or for reasons of fire safety.

Services can pass through the cellular beams or truss.

Systems with decking surface

This arrangement is only possible for certain types of small diameter pipe systems.

Plinth or breast systems Installation of composite façade walls facilitates this arrangement, with ease of service offsets and connections through elimination of constraints imposed by heavy walls.

Systems on floors Raised floors always consist of steel structures. The space created between the floor and the false ceiling allows movement of services with large number of ducts. These offer full accessibility and adaptability.

Figure 6.10 Cellular beams and service integration

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7 STEEL CONSTRUCTION AND SUSTAINABILITY

The preoccupations of the sustainable development are of particular concern for the construction sector, which is responsible for 25% of greenhouse gas emissions and for 40% of the primary energy consumption. They constitute a major stake for all the involved professionals.

It is a question today of designing and of realizing creative projects which integrate values and new techniques. Steel is the mainspring in our quest to improve the quality of our buildings and their impact on our living environment.

General principles are established according to three main considerations: ecological, economical and socio-cultural, although the methods for determining their impact have not yet been agreed on an international scale.

The sustainability of buildings concerns a range of issues related to choice of materials, construction process, occupation and end of life. These issues may be expressed in terms of specific criteria, such as energy materials use, waste minimization, reduction of primary energy use (and CO2 emissions), pollution and other global impacts.

Figure 7.1 Praetorium building in La Défense (Paris) with ‘High

Environmental Quality’ label

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7.1 Life cycle Steel is an excellent solution for conserving raw materials, thanks to its recyclability. It can be infinitely recycled without losing its properties.

Today, the production of steel in Europe consists of 50% recycled metal, reducing the need for ore; for certain products intended for construction, this rate can reach up to 98%. This re-use of the material is in particular made possible by its magnetic properties facilitating the sorting.

For 25 years, the control of energy and the reduction of CO2 emissions during production have led to vast improvements in developing new steel materials and taking into account life cycle of materials and products. The European steel industry has substantially contributed to the energy efficiency and the reduction in CO2 emissions.

Between 1970 and 2005, the European steel industry reduced CO2 emissions by 60%; between 1990 and 2005, this reduction was 21% (source Eurofer). In the same period, crude steel production increased by 11.5% (source Worldsteel for EU15).

Other solutions are already underway to improve these results.

Steel is a neutral material which emits no polluting substance or element that is harmful to the environment or health, even under the influence of corrosion.

Galvanizing and painting (carried out in the factory) are corrosion protection systems that guarantee the durability of steel up to 25 years.

Maintenance of steel is limited to regular follow-up and periodic painting.

7.2 Advantages of steel products for construction An Environmental Product Declaration (EPD) is now a widely developed approach for construction products. Based on ISO 21930[2] the overall goal of an EPD is to provide relevant, verified and comparable information to meet various customer and market needs.

Using life cycle assessments, the steel industry has already provided several EPD for generic products as well as branded systems. The energy and lighting consumption during service life exceeds the embodied energy in the structure.

Thanks to the efficient use of materials, steel construction minimizes waste in manufacture and on-site, because all steel off-cuts and drills are sent for re-cycling into new steel components. Typically, the average steel wastage and re-use is about 2%, in comparison with the European average of 10% for all the products used on-site.

The excellent weight-resistance ratio of the material offers incomparable constructive and architectural possibilities. This performance opens the way to the reducing the weight in buildings, using thin walled structures in the façade. These features offer a large amount of space with light and vast possibilities for architectural integration.

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The association of steel with other materials offers many efficient solutions for thermal and acoustic insulation.

For the envelope, the metallic construction is generally designed with an external thermal insulation; walls are built from industrialized systems, metallic or not (glass, wood, concrete, terra-cotta, plaster, etc.), which offer high levels of thermal performance. The heating and ventilation systems can then be chosen for optimal energy behaviour.

The range of qualities opens the architectural choices and allows the optimized selection of the processes, the materials and the methods of construction, especially by considering the global life of the building to be realized up to its demolition.

7.3 Steel-intensive solutions for buildings For buildings there are several environmental initiatives across Europe. These approaches can be quantitative or qualitative, using variable criteria. However, some subjects are common, but with different treatments, for which steel solutions bring firm answers.

The harmonious integration of the building with its surrounding environment

The choice of a steel frame for a building project allows the designer a large freedom of shape and the flexibility to adapt work to the constraints of the site.

Used for façades or roofing, steel products offer the architect a range of textures, geometries and colours to respond to the most sensitive and the varied of contemporary sites, whether a historical city centre or in the countryside.

Lightness of the structures and the flexibility of spaces

A frame made with columns and beams is typical in steel buildings. Without load-bearing walls, the construction is lighter; the impacts on the foundations and the ground are lesser.

It is also easier to remodel internal spaces according to the changes of use.

A structure with connected components is an efficient solution for vertical extensions as well as in the renovation of an existing building.

Less on-site problems

Steel products and associated elements are industrially made, of high precision. They are delivered with accurate dimensions for on-site assembly. Due to the higher level of pre-fabrication, implicit in steel-intensive constructions systems, speed of construction is increased.

The construction site is transformed, with reduced deliveries, precise and appropriate assembly, less storage and no waste.

Maintenance

Steel solutions provide durability and facilitate cleaning and replacement of components.

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Services (fluids, ducts, etc) are generally placed in the ceiling void. The maintenance and the possible reconfiguration of the services are then facilitated, especially in the presence of cellular beams. This flexibility allows the different levels to be completely refitted.

At the end of life, the demolition consists of a clean dismantling, for a complete recovery of materials.

Re-use of steel profiles

In Western Europe, a study has shown that about 11% of profiles in the construction sector are directly reused after demolition, without remoulding (ECSC Report ‘LCA for steel construction’. Document RT913. July 2002. Steel Construction Institute).

Creating a safe and comfortable internal space

All combinations of wall components can be accommodated.

Steel solutions in combination with additional products contribute to the excellent sound insulation through the ‘mass-spring-mass’ principle.

For thermal comfort, steel allows the design of ‘evolved’ façades, adapted to the various climatic conditions:

Double-skin façades, implementation of a layer of ventilated air,

Fixed or mobile solar control mechanisms

Integration of alternative technologies on steel buildings

Alternative Energy Technologies (AET) are integrated into building design for a wide range of reasons but typically the primary motivators are green aspirations and planning restraints such as ‘Grenelle’, which will require a certain percentage of a building’s energy consumption to be provided by additional benefits from using AET, including renewable energy.

AET provide environmental benefits over the use of standard energy supply. Moreover, they have a very low impact on steel buildings. The main concerns for AETs implantation are:

Plant Room: The location of the plant room and spatial restrictions can impact on the viability of specific technologies

Shading: the shape of the new building may restrict the location of solar PV panels.

Roof Orientation: The orientation and the shape of the roof can be a limitation on energy output, for either solar hot water collectors or photovoltaic panels.

Reliability: If an unproven technology is used then it may not be reliable and so the desired carbon savings cannot be made.

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Table 7.1 Renewable energy sources

Type Comment

Biomass heating

1 Boiler 2 Burner 3 Pump 4 Ash removal 5 Biomass fuel delivery 6 Cold water 7 Hot water 8 Flue gas

5

2

4

6

7

1

8

3

The system requires a basic plant room for the boiler and storage for the fuel. This can be fully integrated in the building, creating a steel storage with a steel frame.

Combined Heat and Power (CHP) 1 Boiler 2 Engine 3 Pump 4 Generator 5 Main gas supply 6 Cold water 7 Hot water 8 Flue gas 9 Electricity

9

2

5

4

6

7

1

8 3

The system only requires a typical plant room, entirely compatible with a steel frame construction for mixed-use developments and sites with high hot-water loads. It is generally suitable for swimming pools, hotels and hospitals,

Ground Source Heat Pumps (GSHPs) 1 Compressor 2 Expansion valve 3 Pump 4 Heat exchanger 5 Electricity in (AC 230V) 6 Hot water supply 7 Cold water return 8 Return to heat source 9 Supply from heat source

5

8

7

6 3 3

4 4

1

2

GSHP’s can be applied anywhere given that there is enough space for plant room and ground loops or wells. Often, areas used for car parks or gardens can be used. All steel buildings are suitable for this technology.

Solar Hot Water Collectors 1 Absorber plate 2 Pump 3 Cold water supply 4 Hot water return

3

1

4

2

Solar Photovoltaics

Solar equipment can be installed on a flat roof without impact on the steel structure using a cantilever, a steel structure to support the panels (however, system weight, wind and damp-proof cloth resistance have to be considered). On a pitched roof, the system can be implemented by using subsidiary steel work, clips or directly integrated in the roofing such as PV tiles or on a façade, with simple rails to allow the fastening.

1 Photovoltaic module

3

1

4

2 DC electricity generation 3 Inverter 4 Electricity

2

Wind Turbines

3 1

2

4

1 Wind energy 2 Turbine blades 3 Generator 4 Electricity

A small scale wind turbine requires little infrastructure for its inclusion; only an allowance for cable ducts from hard standing areas to a suitable plant room. If directly mounted on steel frame buildings, it is essential to consider the additional loads, vibration and noise. Small wind turbines can be suitable for steel buildings, such as commercial buildings, aircraft hangars, or industrial buildings as they are best located in a clear wind stream, away from obstructions and surface roughness.

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8 CONCLUSION

Thanks to its outstanding mechanical performance, to the freedom of technical prowess it affords, to its flexibility of use in different types of buildings, to its plastic and aesthetic potential and the creativity it inspires, steel has a natural place in the pantheon of materials for architectural design.

When an architect chooses steel, he knows this is a choice of no small consequence. First this choice implies rigorous design, awareness of the functionality of each of the elements that make up the design, and analysis of all stages in the building process – from drawing board to routine management of the completed project. Second, the choice is an expression of affirmation, of putting ones mark on a design, a way of conceiving and perceiving, a willingness to contribute to the urban landscape, to integrate with light and air into the urban fabric. Steel is a form of expression which gives meaning to architectural design.

Choosing steel to design a multi-storey building is to choose a material which offers low cost, strength, durability, design flexibility, adaptability and recyclability. It also means choosing reliable industrial products which come in a huge range of shapes and colours; it means rapid site installation and less energy consumption. It means choosing to commit to the principles of sustainability. Infinitely recyclable, steel is the material that reflects the imperatives of sustainable development. In conclusion, choosing steel means choosing a greater freedom of construction, of architecture. It means injecting style into the buildings and the cities of tomorrow.

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REFERENCES

1 EN ISO 14713 Zinc coatings. Guidelines and recommendations for the protection against corrosion of iron and steel in structures.

2 ISO 21930:2007 Sustainability in building construction. Environmental declaration of building products

MSB01 Architects Guide 2010-08-05 PDF

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